GChem: Bonding and Intermolecular Forces and Thermodynamics

Question 1

The more S character the _____ shorter/longer the bond

Answer 1

The shorter the bond (stronger the bond)

BUT only when comparing the same types of bonds (ex. compare C-O bonds to each other)

Question 2

Coordinate covalent bond and body example

Answer 2

B/w atoms with lone pair and e- deficient species (lewis acid/electrophile)
Lewis acids: B, (transition) metal cation, BF3 = lewis acid b/c wanted a complete octet
When one atom donates BOTH of the shared e- in the bond
Between lewis base/ligand/nuecleophile and lewis acid/electrophile
A lewis base is a molecule or ion that donates a pair of nonbonding electrons so it must have them in the first place
Ex. In hemoglobin, ligand chelate and O2 binds Fe2+
BH4- CANNOT behave like lewis base

Question 3

Ionic bonds - the strength of the bond is proportional to… and decrease as ions get closer/farther apart

Answer 3

The strength of the bond is proportional to the charges of the ions and decrease as ions get farther apart
Ex. MgS vs NaCl
MgS - Mg2+ S2-
NaCl - Na1- Cl1-
so MgS “bond” expected to be four times stronger than NaCl bond

Question 4

Orbital geometry/molecular geometry (state bond angle for each) vs shape of molecule

Answer 4

Orbital geometry/molecular geometry = linear (180º), trigonal planar (120º), or tetrahedral (109.5º)

Shape: bent, trigonal pyramidal

Question 5

How many sigma and pi bonds are in a triple bond?

Answer 5

one sigma, two pi

Question 6

List the strengths of IMFs - there are 5

Answer 6

H-bonds
Ion-dipole
dipole-dipole
dipole -induced dipole 
london dispersion

Question 7

For IMFs, a _____ more/less polar molecule generates a stronger force and a molecule with ______ more/less e- and ____ larger/smaller size generates a stronger force bc it’s _____ more/less polarized

Answer 7

Pretty sure the polarized rule works for all IMFs
more
more
larger
more
Ex. F2 and Cl2 exist as gases and but Br2 is liquid and I2 is solid bc strength of dispersion forces increase as atomic size increases.

Question 8

In order to have a hydrogen bonding, you need…

Answer 8

Bond between H and N,O, or F and another molecule must have a lone pair of e-s on an N,O, or F atom.
Ex. water to other waters

Question 9

Substances with stronger IMF have:
\_\_\_\_bp
\_\_\_\_mp
\_\_\_\_viscosities
\_\_\_\_vapor pressure

Answer 9

greater bp and mp
greater viscosity
lower vapor pressure (more easily it evaporates and liquids with high vapor pressures are volatile)

Question 10

*Ionic Solids

What 2 factors influence its strength?

Answer 10

Electrostatic attraction between cations and anions in a lattice structure (most solid at room temp)
The intermolecular bonds are the same as the intramolecular bonds! All ionic
Magnitude of ion charges (biggest effect)
Size (the smaller the ions, the more attracted to each other)

Question 11

(I skipped)

Network Solids

Answer 11

Connected in lattice of covalent bonds - super strong
tend to be hard solids at room temp
Ex. diamond and quartz

Question 12

Metallic solids

conduction electrons

Answer 12

A sample of metal can be thought of as a covalently bound lattice of nuclei and their inner shell electrons surrounded by sea/cloud of electrons Freely moving electrons called conduction electrons
SO EXCELLENT CONDUCTORS OF ELECTRICITY, MALLEABLE, DUCTILE
Almost all solid at room temp
vary in strength

Question 13

I skipped

Molecular solids

Answer 13

Particles at the lattice points of crystals of molecular solid are molecules held together by one of three types of intermolecular interactions - hydrogen bonds, dipole-dipole forces, or london dispersion so typically has lower mp and bp
often liquids and gases at room temp and start to be more solid as strength of their intermolecular forces increase

Question 14

Rank the following from highest to lowest bp:
I  H2SO4
II NH3
III CO2
IV H20

I>IV>II>III
II>I>IV>III
I>III>IV>II
IV>III>I>II

Answer 14

A is the answer
I and IV are liquids at room temp and II and III are already gases!

H2SO4 and H20 have hydrogen bonding but H2SO4 is larger (can have greater polarity) and more sites to accept H-bonds from surrounding molecules

Question 15

When energy flows into a system from the surroundings, the energy of the system _____ increases/decreases and the energy of the surroundings ____increases/decreases

Answer 15

increases

decreases

Question 16

Enthalpy

What is the sign when a bond is formed? When broken?

Answer 16

heat energy that is releases or absorbed when bonds are broken and formed during a reaction that’s run at constant pressure. The symbol is H
When a bond is formed, energy is released ∆H<0 (heat flow out of the system
Energy must be put into a bond in order to break it ∆H>0 (heat flows into the system)

Question 17

Heat of reaction

Answer 17

Enthalpy change ∆H

Question 18

How much heat is produced when 16 g of oxygen gas reacts with excess methanol?
2CH3OH + 3O2 -> 2CO2 + 4H2O ∆H = -1352 kJ

Answer 18

First have to convert 16g of O2 to moles BUT for moles calculation must remember to do 16g/2(16) have to multiply 16 by 2 bc have to do this when see subscript
then continue with calc
solution page 125 of GChem
225kJ

Question 19

Standard conditions vs standard temperature and pressure (STP)

Answer 19

Standard conditions (like room temp) are 298ºF/25ºC, 1 M solution, 1 atm

STP - 0ºC
1 atm (pressure)
1 mole of gas will take up 22.4 L of the volume of the container.

Question 20

Equation for heat of formation

Answer 20

∆Hºrxn = (Σn × ∆Hºf,products) -

Σn × ∆Hºf,reactants

Question 21

∆Hºf is 0 for elements in their natural state -> natural phase and diatomic at standard conditions
Name diatomic elements and phase at standard temp

Answer 21

Have Hydrogen (gas)
No     Nitrogen (gas)
Fear  Fluorine  (gas) 
Of      Oxygen  (gas)
Ice     Iodine (gas) 
Cold  Chlorine (gas)
Beer  Bromine  (LIQUID)

Question 22

Hess’s Law 2 things to remember when adding enthalpies up

Answer 22

Basically add two chemical equations to get the right one
If a rxn is reverse, sign of ∆H is reversed
If an equation is multiplied by a coefficient, then ∆H must be multiplied by that same value

Question 23

Equation for ∆Hrxn? (third reaction)

Answer 23

∆Hrxn = Σ(BDE bonds broken) - Σ(BDE bonds bonds formed)
so if stronger bonds are being formed than those being broken, then ∆Hrxn will be neg - more E is released than supplied and rxn is exothermic

Question 24

Equation for ∆Hrxn? (third reaction)

Answer 24

BDG -> bond dissociation energy
∆Hrxn = Σ(BDE bonds broken) - Σ(BDE bonds bonds formed)
so if stronger bonds are being formed than those being broken, then ∆Hrxn will be neg - more E is released than supplied and rxn is exothermic

Question 25

∆S =

What factors influence ∆S?

Answer 25

∆S = Sproduct - Sreactants
In terms of who has more entropy:
Gases>Liquids>solids
Particles in solution have more entropy than undissolved solids
Two moles of substance have more entropy than one mole
The value of ∆S for a reverse rxn has the same

Question 26

Equation for ∆G

What does it mean when ∆G is pos, 0, neg?

Answer 26

∆G = ∆H -T∆S
pos -> nonspontaneous
0 -> at equilibrium
neg -> spontaneous

Question 27

The differencen between exothermic/endothermic vs exergonic/endergonic

Answer 27

exothermic/endothermic for ∆H

exergonic/endergonic for ∆G and when looking at graphs to see if prod are lower than reactants etc

Question 28

Ea

Answer 28

Ea is the extra E the reactants required to overcome the activation barrier, and determines the kinetics of the reaction
The higher the barrier, the slower the reaction proceeds to equilibrium

Question 29

What happens to ∆G, ∆H, and ∆S for the reverse rxn?

Answer 29

Same magnitude, opposite sign

Question 30

Heat(enthalpy) of vaporization

Answer 30

Heat to evoke evaporation phase change

Question 31

sublime

Answer 31

convert a solid to a vapor

Question 32

Heat of fusion?

Answer 32

When a solid undergoes melting or freezing

Conversion between liquid and solid

Question 33

What is greater, the heat of fusion or heat of vaporization?

Answer 33

For all substances, the heat of vaporization is substantially higher than the heat of fusion. Much more energy is required to change the state from a liquid to a gas than from a solid to a liquid.

Question 34

*What are units for mass of a solvent? (technically two different units mean the same thing)

Answer 34

1 mL = 1 g

Question 35

Amphiphilic (amphiphatic)

Answer 35

A molecule having both hydrophobic (nonpolar) and hydrophilic (polar) regions

Question 36

Urea -> what does it do?

Answer 36

Based on its structure, urea, CO(NH2)2, will interact with the polar moieties of a protein via hydrogen bonding, which include the peptide backbone and polar residues (charged or uncharged). By disabling intramolecular hydrogen bonding urea is capable of stabilizing the denatured state of a protein